Amorphous Silicon Anodes

Overview

In this work we formulate and numerically implement a fully-coupled diffusion-deformation theory for amorphous Silicon anodes. The theory accounts for transient diffusion of lithium and accompanying large elastic-plastic deformations. The material parameters in the theory have been calibrated to experiments of galvanostatic cycling of half-cells composed of an a-Si thin-film anode deposited on a quartz substrate, which have been reported on the literature.

We have applied our numerical simulation capability to model galvanostatic charging of hollow a-Si nanotubes whose exterior walls have been oxidized to prevent outward expansion. We show that the results from our numerical simulations are in good agreement with the experimentally-measured voltage vs. SOC behavior at various charging rates (see figure below).

Through our simulations, we identify and quantify two major effects of plasticity on the electrochemical performance of these a-Si anodes:
– For a given voltage cut-off, plasticity enables lithiation of the anode to a higher SOC by reducing the stresses generated in the materials.
– Plastic deformation can account for a significant percentage of the energy dissipated during the cycling of the anode.